Upon manufacturing heat exchangers having tubes engaged into tube-plates, it is of usual practice to proceed to an expanding operation of the ends of the tubes consisting in engaging a punch into the duct delimited by each tube to press the outer wall of said tubes against collars which usually flange passages for the tubes in each tube plate.
Said operation results in opening the mouth of the tubes to facilitate welding or brazing of the tubes with the collars of the tubes plates, but it does not ensure a strong mechanical connection between the tubes and the tube plates as long as the heat exchanger is not yet welded or brazed. It then occurs frequently during the handling operations of the heat exchanger that the tubes plates are moved from the ideal position they are supposed finally to occupy in the finished heat exchanger. Moreover, when the apparatus is completed, i.e. after welding or brazing is completed all the mechanical stresses applied between the tubes and the tube plates are supported only by the welds.